A high power rotary transformer may be utilized to transform electrical power from one power grid operating at one frequency to a second power grid operating at a second frequency. U.S. Pat. No. 5,953,225 issued Sep. 14, 1999 to Larsen discloses a rotary transformer that includes a power recovery system to recover and apply to the transferee grid a power differential attributable to mechanical power channeled to a rotatable shaft of the rotary transformer.
Another such rotary transformer assembly is disclosed in Canadian patent application serial number 2,351,895 published Dec. 30, 2001 to Martin and Rehder. This rotary transformer assembly utilizes three phases of isolated bus duct passing through the center of the rotating shaft to connect the rotor of the rotary transformer to one of the two power systems between which the rotary transformer transforms the electrical power from one system through a stator to the other system operating at a slightly different frequency. Both shaft sections are coupled together by a coupling flange. The rotor of the rotary transformer is supported on the lower shaft section. The power recover system includes a drive motor connected to the upper shaft section between the two sets of leads of the bus duct. The drive motor applies torque to the upper shaft portion to recover power relatively close to lower exit lead openings for the bus duct.
In recent developments, it has been determined that it is more preferred to have the bus duct extend through the lower shaft as well the upper shaft so that the upper shaft is not weakened when the drive motor applies torque to the upper shaft. This has further resulted in a need for modifications to the drive motor coupling to the upper rotor shaft to compensate for a shaft that might otherwise be damaged, weakened, or broken during a short circuit of the drive motor or other short circuit conditions